Hydraulically controlled steering mechanism for aircraft



March 17, 1953 H. B. SCHULTZ HYDRAULICALLY CONTROLLED STEERING MECHANISM FOR AIRCRAFT 4 Sheefs-Sheet 1 Filed May 2, 1947 j v I \w\ .1 Y Q m W E m 6 m \N A mw m a mu \J A & fi Q Q Q .0 N 3 m 3 mW m w H Q & Mk g Q u w M n n \N\ S Q g w I m" S FHAH 4 3 3 WV K 3 N m 3 g s v fig E March 17, 1953 H. B. SCHULTZ 2,631,795

HYDRAULICALLY CONTROLLED STEERING MECHANISM FOR AIRCRAFT 4 Sheets-Sheet 2 Filed May 2, 1947 h) l A fa g un:

INVENTOR. gimp fifmazfz A TTOIZNE Y March 17, 1953 B SCHULTZ 2,631,795 HYDRAULICALLY CONTROLLED STEERING MECHANISM FOR AIRCRAFT Filed May 2, 1947 -4 Sheets-Sheet 4 Un -m.

IN V EN TOR.

@1 00 5 Jowz'z A 7' TOENE Y Patented Mar. 17, 1953 HYDRAULICALLY CONTROLLED STEERDIG MECHANISM FOR AIRQRAF'E Harold B. Schultz, South Bend, 1nd,, assignor to Bendix Aviation Corporation, South Bend, a corporation of Delaware Ind Application May 2, 1947, Serial No..745,676

3 Claims.

Thisv inventionrelates generally to steering mechanisms and more particularly to a steering .device forthe nose wheel of an airplane.

' Theinventlon.comprehehds as one of its ob jects the provision of a steering apparatus for the nose wheel of an airplane. wherein the wheel is remotely controlled through the hydraulic actuationof a valve.

.An objectof the invention resides in the provision of apower steering apparatus for. the nose wheel of an aircraft in which the power for steering isobtained from'an openhydraulic system and the .control .of this power is through the medium of a'closed hydraulic system.

A further object of the invention is to provide a steering apparatus for actuating a member to be steered and including'two independent hydraulic systems one of which supplies power for moving said member and the other which controls the power.

A still more important object of the invention embraces a hydraulic steering apparatus connected to a steered member in a manner to impart movement thereto whereupon the. cause producing said movement diminishes with the movement of the steered member.

The above and other. objects and features of the invention will be apparent from the. following description of the apparatus taken in connection with the accompanying drawings which form a part of this specification, and in which:

. Figurel exemplifiesthe complete steerin apparatus;

Figure 2 is a longitudinal sectional view of the actuator of the invention with parts in elevation;

Figure 3 is a transverse sectionalview of the actuator of Figure 2;

. Figure 4 is aview in longitudinal section of the receiver shown in Figure 1; and.

;Figure 5 is a longitudinal sectional view of the hydraulically actuated valve-of Figure 1.

Referring to Figure l of the drawingsreference numeral l0 designates a landing gear for an aircraft, not shown, having an actuator l2 mounted thereon, and steerably connected to. a steered member or wheel [4 pivotally positioned on an axle I6 integralwith a tube l8 rotatable about its axis andtelescoped into a larger tube to which the actuator. is fixedly secured.

The steering apparatus includes the actuator l2, operatively connected to a follow-up motor or receiver 22 which is interconnected through conduits 26, '28, 39, 32,34 and 36 with a transmitter 13.8. A compensator 39 is interposed between consiuits 312 and, and 3lland- 36"tpfcompensate the system for pressure changes due to temperature variation of the fluid. A hydraulically actuate valve lli is interposed between conduits 26 and 3t, and 28 and 32, for controlling fluid under pressure to .the actuator from pump 32, and the return of fluid to reservoir ii. Conduits i6, 48, 59 and -52 interconnect the actuator to the pump and reservoir through the hydraulically actuated valve All The pump 52 puts fluid under pressure in an accumulator 54 which stores the fluid until a predetermined pressure is reached at which time an unloading valve 55 is operated to by-pass fluid to the reservoir 44.- A filter 58 is interposed in the line between the reservoir and pump.

- The wheel it is rotatably carried by the axle it which is integral with the tube 53 which telescopes into the larger tube 20. The inner tube 1% slides and rotates freely in the outer or larger tube 2:] to permit pivoting about an axis normal tothe wheel axlefor steering. A collar 60 fits over one end ofthe outer tube 20 and bears at one end on a flange E52; integral therewith. At its other endthe collar bears against a fitting 63 which is securely keyed to the.tube and held against axial movement by a nut 6d. The collar is free to rotate around the outer tube and is formed'with a lever 68 to which is connected one end of a link 67, the other end of which is connectedto a lever 69 of the actuator 2 for imjpartingrotation to the collar. A second collar l! is fixedly secured to the inner tube 1 8. A scissors level 63 connects the rotatable collar with the collar H to thereby enable the tubes to slide axially with respect to each other and to provide for rotation of; the inner tube through rotation of the collar so. The fitting 63 supports the actuator-through a bracket it. A clamp 12 is secured to the-outer tube. 20 and supports the receiver 22. The clamp '72 also provides a support for the actuator 12 through a bracket 73.

' As best shown in Figures 2 and 3, the actuator I2 is of unitary construction and comprises a hydraulic motor M drivably connected to a sector '76 splined ;or otherwise securely fastened to a shaft; The shaft is connected at one end to 1 the receiver and at the other end to link 61, and is rotatably supported in roller bearings disposed in each end of cylinder 80. The bearings are pressed into supporting rings- 8| which are held in po ition in the ends of the cylinder by cap screws 83 which threadedly engage the rings.

- The hydraulic motor includes a cylinder 82 having its axis at right angles to the axis of cylinder 86. The walls of the cylinders and 82 have openings 84 and 36 respectively, therein,

which are in registry when the cylinders are welded in assembled relationship. The sector It projects through the openings 84 into the cylinder 82 where the sector engages the teeth of a rack 88 carried by a piston 90. The admission of fluid under pressure to one end of the motor cylinder 82 and simultaneously exhausting 'fiui'd from the other end of the cylinder moves piston 90 and in so doing imparts rotative motion to shaft 18 through the sector I6. Rotation of shaft IS in turn rotates the collar 60 through the link 61, whereby the inner tube I8 is turned around its axis to change the direction of wheel I4.

The hydraulically actuated valve of Figure 5 comprises a body 92 with a bore 94 therein. An

inlet port 95, cylinder or working ports 98, and return port I330 are formed in the body member and open into the bore at axially spaced positions therein. Sleeves I02 are located in opposite ends of bore 94 to receive plungers I34 coaxially arranged in opposing relationship" soas to divide the bore into end chambers I06 and I38 and a central chamber I' I 3. The ends or the bore are closed by cap-s I'I2 interioi'ly threaded to engage the body member. The sleeves are securely held in position in the borebetweri the cap H2 and shoulders H4 and IIS'. spacers I I8 are" interposed between one end of the sleeves and the shoulders H4 and H3. The sleeves are provided with valve seats I2 arranged in the bore between the inlet port and the" cylinder ports; The sleeves are bored radially at ['22 so" to register with the cylinder ports to thereby communicate these ports with the bore. The caps I I 2 are provided with male connections I24 constituted to be connected to a pressure source; whereby the end chambers I 86 and I08 are: subjected to differential pressure which acts on the remote ends of plungers I'M.- A rod I26 extends through the bore and is carried at its ends by the adjacent or inner ends of the plunger-s I134. The length of rod I26 is such that when the ressures in the end chambers I06 and IE8 are equal the valve heads I34 will be off valve seats I32, as shown in Figure- 5. I'he arrangement of the rod and plungers is such that when a differential inpfesSur'e' occurs in the ends of the bore the plungers and rod tend to move as a unit, that is, movement of any one of the plungers inwardly tends to move the other plunger outwardly. The plungers are limited on their axial outward travel by shoulders I28 formed on the sleeves to engage enlarged ends 1 5i) of the plui'lgeis; 7

To control flow" between the cylinder ports 98 and the return port IOU, which opens into the central chamber, the enlargedheads I31] on the adjacent or inner ends of the filu'iigei's are equipped with Valve seats I32 which cooperate valve heads I34 formed on two holld'w valve members I35 slidably interposed services the adj scent ends of the piun ers in coaxial redatiohship. The valve members are urged dfito the valve seats 1120 located in the bore between the inlet and cylinder ports to thereby cut off communication between these ports. A spring I38 has it's ends in engagementwith the adjacent ends of the valve members to thereby urge the same cuts the valve seats I20.

With an increase in pressure in chamber I05 and a concurrent decrease in pressure in chamber I98, the plunger on the left will move to the right where its valve seat will be engaged by the valve head of the hollow valve member an the left to cut ofi communication between the cylinder port on the left and the; return port I00.

Continued movement of the plunger unseats the left hollow valve member from valve seat I20 to establish communication between the inlet port and the left cylinder port. Movement of the plunger on the left in the aforementioned direction moves the plunger on the right away from itsyalve seat to thereby allow for an increase in flow between the" cylinder port on the right and the return port. The flow between the cylinder and return ports being through the hollow valve member.

The transmitter 38, receiver 22, temperature compensating mechanism 39 and interconnecting conduits provide a closed hydraulic system for operating the hydraulic valve 40. The end chambers I38 and IE8 of the valve are connected to conduits Z8 and 32, and 28 and 30 respectively. The transmitter unit comprises a cylinder I49 having a piston I4I therein, dividing the cylinder into two chambers, one at each end thereof. The piston I4I has a rack I42, integral therewith. A shaft I43 is rotatably carried by the cylinder transversely thereof and provided with gears I44 and I45 secured to opposite ends of the shaft. A steering. device or Wheel I46 15 splined or otherwise secured to one end of a shaft I41 having a pinion gear I48 suitably secured thereto at the other end for driving engagement with gear I45 to thereby impart reciprocal motion to piston I4I through rotative motionof the wheel. A conduit I49 connects the ends of the cylinder I46. A bleed or centering valve I50 is located in the conduit M9 for manual operation to thereby control communication between the ends of cylinder hill to permit centering the piston HI therein.

The receiver unitincludes a cylinder I5I having a piston I52 reciprocal-1y positioned therein and dividing the cylinder into a pair of opposed chambers. The cylinder body is formed with openings I53 and I54 in its ends for connecting the receiver with the transmitter through conduits 25- and 23 which in turn are in hydraulic circuit with conduits 33 and 32 respectively. A piston rod I55 is carried by the piston and extends through the ends of the cylinder I5I to thereby provide equal effective areas on the opposite sides of the piston. As best shown in Figure 1, the piston rod is operatively connected to the shaft 78 of the actuator and a passage I53 connects the ends of the cylinder I5 I. A manually operated valve I 51 controls communication between the ends of the cylinder to permit centering the piston I5I as hereinbefore pointed out in regard to piston I4I of the transmitter.

' With reference to Figure 1,- it is obvious that the areas of the ends of piston I41 of the transmitter are greater than the corresponding areas of the ends of plungers I34 of the hydraulically actuated valve 43. It therefore requires a greater pressure in 34 and 36 to move the plungers than to move the piston. Hence any buildup" in pressure in these lines due to shock loads on the wheel I4 will tend to move the piston in a direction to follow up the receiver piston I52, thus relieving the pressure in the lines. This response by the transmitter to a buildup in pressures in lines 34 and 36 as aforementioned precludes actuation of the valve mechanism 4!] during normal nonsteering conditions.

To compensate for pressure changes in the closed hydraulic system due to variation in temperature of the fluid in the system the compensating mechanism 39 is provided. The mechanism includes a valve member I58'seated in a passage I59 which communicates conduits 30 and 88 with a reservoir I60, the interior of which is divided, by a flexible diaphragm I8I into an upper chamber I62 into which air is pumped under pressure, and a lower chamber I3 in communication with passage I59, whereby any change in volume of fluid in the system is accounted for in the reservoir I50. The valve member I58 has a stem I 64 integral with a head I05 which is urged onto a valve seat I06 located in the passage I59 by a spring IBlto normally cut off communication between the chamber I83 and the lines 30 and 36. The stem of the valve member has one end subjected to the fluid under pressure in lines 32 and 34. A seal I68 encircles the valve stem to prevent leakage between the lines 34 and 36 axially along the valve stem. It will be noted that the effective annular area of the valve head formed between the valve seat and valve stem and on which the pressure in lines 30 and'36 acts when the valve member is seated, is equal to the effective area of the valve stem I 84 on which the pressure in lines 32 and 34 act. Inthe present illustration the spring I6! is selected to exert a force on the valve member equal to substantially one-half the total operating force required for the system. Actually, however, the total force holding the valve member I58 on its seat is the summation of the force of the spring force I6! plus the pressure of the fluid in chamber chamber to the lines but prevent flow in the opposite direction. The conduit 48 intersects'the passage I10 and is in communication with the fluid source used for operating the actuator I2. A check valve I I2 is located in the conduit 48 to permit the flow of fluid into conduits 30 and 35 but prevent flow in the opposite direction. A spring I13 is interposed between the check valves I10 and H2 to urge them onto their seats. Manually controlled valves I15 and I16 are located in conduits 46 and-48 and normally disconnect the closed hydraulic system from the accumulator 54 and reservoir 44.

In the steering apparatus herein exemplified a closed hydraulic system controls a hydraulically actuated valve which is constituted to'in turn control fluid under pressure from a second and open hydraulic system, whereby power steering is accomplished.

Operation of the steering apparatus is asfollows:

With the parts of the steering apparatus in the positions indicated in the various figures, the

pressures in the lines 30 and 35, and 32 and 34 of the closed hydraulic system are substantially balanced across the ends of the pistons I41 and I52, and consequently the pressures in the end chambers I00 and I08 are equal. Under these conditions the hydraulically actuated valve 40 is closed to thereby out 01f fluid under pressure to the actuator from the pump or accumulator. The parts of the valve are now positioned to communicate the ends of the actuator hydraulic motor with the reservoir. Communication between the reservoir and actuator is through conduits 50, 52, cylinder ports 98, the hollow valve members I 30, return port I00 and return conduit 46.

To accomplish steering, the wheel I46 is rotated in the desired direction. If for example, the steering wheel I40 is rotated in a manner to move piston I4I to the left the pressure in 6 conduits '28, 32, 84, the left end of the'hydraulic valve 40, and in the left end of the receiver 22, as viewed in Figure 1, will be increased and at the same time the pressure in conduits 28, 30, 36, the right end of the hydraulic valve, and in the right end of the receiver will be reduced, whereby a differential pressure is created in chambers I06 and I08. Since the increase in pressure is in chamber I05 the plungers I04 will be moved to right so that the valve head I34 engages the valve seat I32 to cut oif communication between the left cylinder port 98 and the return port I00. Continued movement of the plungers to the right unseats the left hollow valve member from seat I20 to thereby establish communication between the inlet port and-left cylinder port. The plunger on the right has also moved to the right so that its seat I32 has moved farther away from valve head I34 to permit uninterrupted flow between the cylinder port on the right and the return port.

With the valve ports in this position, fluid under pressure from the pump will act in the end of cylinder 82 toward the reader, moving the piston away from the reader and producing clockwise rotation of the sector 16 and shaft I8. With the crank arm 66 connected to one end of shaft end of the receiver is put under pressure which tends to move piston I 52 but since it is operatively connected to the sector shaft I8 the receiver piston is held from movement. -However, this same pressure which acts in the receiver also acts in the hydraulic valve to move the plungers and consequently the valve members to thereby establish communication between the actuator motor and the pump or accumulator to cause rotation of the sector and shaft. Rotation of the sector shaft 13 moves the receiver piston in the direc tion of its intended movement as determined by the end of the receiver cylinder in which pressure acts when the transmitter is operated. Any movement of the sector shaft relieves the pressure in the receiver cylinder and also in the ends of the hydraulic valve. This arrangement provides a follow up control which tends to equalize the pressure differential acting in chambers I06 and I08 and on the remote ends of the plungers.

Although this invention has been described in connection with certain specific embodiments, the principles are susceptible of numerous other applications that will readily occur to persons skilled in the art. The invention is, therefore, to be limited only as indicated by the scope of the appended claims.

Having thus described the various features of the invention, what I claim as new and desire to secure by Letters Patent is:

l. A power steering apparatus for an aircraft equipped with a steered wheel, said apparatus comprising a hydraulic actuator connectible to the steered wheel, a fluid pressure source, a reservoir for fluid, conduits interconnecting the actuator with said source and reservoir, a closed hydraulic system including a steering device which performs the function of a transmitter for putting fluid in said closed system under pressure, a receiver in the closed system, a valve mechanism located in said conduits and having hydraulic connections to said closed system, and a mechanical connection between the actuator and receiver, said steering device constructed and arranged to respond to lower differential pressures than the valve mechanism when said pressures are developed in said closed system due to shock loads applied to the steered wheel, said valve mechanism having a neutral position in which communication is out ofi between said source and said actuator and established between the latter and said reservoir to thereby permit unimpeded castering of said steered wheel at times of non-steering, said valve mechanism being movable from said neutral position in response to a pressure differential in the closed system created by movement of said steering device to thereby establish communication between said source and said actuator, said receiver being unresponsive to the pressure differential created in said closed system but responsive to movement of said actuator to thereby equalize the pressure differential in said closed hydraulic system whereupon the valve mechanism is returned to its neutral position.

2. A power steering apparatus for aircraft equipped with a steered member, said apparatus comprising a hydraulic actuator connectible to the steered member, a closed hydraulic system including a steering device for putting fluid in said closed system under pressure, a receiver in said closed system, a connection between said receiver and actuator, and a, valve mechanism responsive to a differential in pressure in said closed system for controlling fluid under pressure to said actuator, said valve mechanism being interconnected with said closed hydraulic system, conduits connecting said valve mechanism to the actuator, said valve mechanism being provided with two openings, one of which is connectible to a fluid pressure source and the other of which is connectible to a reservoir, said valve mechanism having a neutral position in which communication is cut off between said actuator and the opening connectible to said source and established between said actuator and the opening connectible to said reservoir, said steering device constructed and arranged to respond to lower differential pressures than the valve mechanism when said pressures are developed in said closed system due to shock loads applied to the steered wheel to thereby provide an open fluid circuit to the actuator so that the steered member is free to move during non-steering.

3. A power steering apparatus for an aircraft wheel, said apparatus comprising a hydraulic actuator connected to the wheel, a steering device, a fluid pressure source, a reservoir for fluid, conduits interconnecting the actuator with said source and reservoir, a closed hydraulic system including said steering device which performs the function of a transmitter for putting fluid in aid closed system under pressure, a receiver in the closed system, a valve mechanism located in said conduits and having hydraulic connections to said closed system, and a mechanical connection between the actuator and receiver, said steering device and valve mechanism each being provided with areas on which act differential pressures developed in said closed system due to shock loads applied to said wheel, the areas of the steering device being greater than corresponding areas of said valve mechanism, said valve mechanism having a neutral position in which communication is cut off between the said source and said actuator and established between the latter and said reservoir to thereby permit unimpeded castering of said wheel at times of nonsteering, said valve mechanism being movable from said neutral position in response to a pressure differential in the closed system created by movement of said steering device to thereby establish communication between said source and said actuator, said receiver being unresponsive to the pressure difierential created in said closed system but responsive to movement of said actuator to thereby equalize the pressure differential in said closed hydraulic system whereupon the valve mechanism is returned to its neutral position.

HAROLD B. SCHULTZ.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 897,907 Lang Sept. 8, 1908 2,030,986 Havill Feb. 18, 1936 2,236,467 Clench Mar. 25, 1941 2,252,660 Kulikoff Aug. 12, 1941 2,260,979 Morin Oct. 28, 1941 2,397,270 Kelly Mar. 26, 1946 2,458,736 Rockwell Jan. 11, 1949 FOREIGN PATENTS Number Country Date 702,983 Germany Feb. 25, 1941 

